Symmetry-Based Microscopic Theory of the Unconventional Pairing Mechanism in La${}_5$Ni${}_3$O${}_{11}$

Abstract

Recent experiments report high-temperature superconductivity in the hybrid nickelate ${\mathrm{La}}_5{\mathrm{Ni}}_3{\mathrm{O}}_{11}$, which is composed of alternating stacks of bilayer ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$ and monolayer ${\mathrm{La}}_2{\mathrm{NiO}}_4$. However, the superconducting transition temperature $T_c\approx 64\mathrm{K}$ for ${\mathrm{La}}_5{\mathrm{Ni}}_3{\mathrm{O}}_{11}$ is remarkably lower than the $80\mathrm{K}$ observed for pressurized ${\mathrm{La}}_3{\mathrm{Ni}}_2{\mathrm{O}}_7$. Thus, an unified microscopic theory is required to address the difference in the pairing mechanisms between these systems. Here, we develop a phenomenological symmetry-based approach to systematically analyze the low-energy physics in ${\mathrm{La}}_5{\mathrm{Ni}}_3{\mathrm{O}}_{11}$, which is obtained by a charge self-consistent density functional theory plus dynamical mean-field theory method. We show that the superconductivity in ${\mathrm{La}}_5{\mathrm{Ni}}_3{\mathrm{O}}_{11}$ exhibits a two-gap nature, consisting of a leading interlayer pairing between the $d_{z^2}$ orbitals and a subleading intralayer pairing between the $d_{x^2-y^2}$ orbitals. The reduction of $T_c$ can be attributed to the diminished contribution of the interlayer pairing, as reflected by the hopping parameter ratio $|t_{\perp }^z/t_{\parallel }^x|$. Base on this unified picture, we discuss the possible pairing mechanism and the role of $\gamma$ pocket for the superconductivity in the bilayer NiO${}_2$ planes of nickelate superconductors.

5 pages, 4 figures